Integrated Master in Dentistry

Margarida Casau*

Advisor:

Paulo Palma*, DMD MhS

Co-advisor:

João Miguel Santos*, DMD MS PhD

* Faculty of Medicine, University of Coimbra

Address: Área De Medicina Dentária, Av. Bissaya Barreto, Bloco De Celas,

Coimbra, Portugal, amgcasau@gmail.com

Coimbra, 2013

Evaluation of root-end preparation with two

different ultrasonic tips

iii

INDEX

ABSTRACT .................................................................................................................................iv

INTRODUCTION ........................................................................................................................ 5

MATERIALS AND METHODS.................................................................................................. 7

DISCUSSION ............................................................................................................................ 15

CONCLUSIONS ....................................................................................................................... 24

AKNOWLEDGMENTS ............................................................................................................. 25

ANNEXES .................................................................................................................................. 26

BIBLIOGRAPHY ....................................................................................................................... 28

iv

ABSTRACT

Introduction

The development of new instruments, materials and techniques has significantly

enhanced the treatment outcome in periapical surgery. In order to obtain a better

prognosis, a good apical cavity must be accomplished.

The aim of this study was to evaluate the time requirements and features apical cavity

preparation performed with different ultrasonic tips from CVDentUS®: model TOF-2 and

a prototype tip.

Materials and methods

Thirty-two freshly extracted single-rooted teeth were selected, cleaned, mechanically

prepared, obturated. After apicoectomy, teeth were randomly divided into group 1

(TOF-2 tip) and group 2 (prototype tip), and the root-end cavity preparation was

performed according the group. The preparation time was recorded.

Photomicrographs taken before and after apical preparation were coded and evaluated

by two examiners. They assessed: the number, type and location of root surface

cracking; the quality of root end cavity margins; and the presence of debris. Statistical

analysis was carried out with Wilcoxon, Mann-Whitney and binomial tests and

Spearman's rank correlation coefficient, using a software package (SPSS).

Results

Three types of microcracks were observed: intracanal, extracanal and intradentine.

There was a significant difference among TOF-2 and prototype tips regarding the

number of microcracks after apical preparation. There was also a statistical significant

difference regarding the location of cracks – 87% were observed in the widest part of

the root.

No significant differences were found regarding “marginal integrity”, “quality walls” and

mean instrumentation time between the two groups.

Conclusion

In conclusion, the best results were obtained when TOF-2 tip was used for root-end

cavity preparation. Good “marginal integrity” and “quality walls” can be achieved with

both tips tested.

KEYWORDS: apical surgery / root-end cavity preparation / root-end cavity

evaluation/ ultrasonic retrotip / CVD tips / retropreparation

5

INTRODUCTION

Nowadays, the success rate of orthograde root canal therapy is high (85% to 95%),

and it is frequently applied to treat inflammation or necrosis of the contents of the root

canal (1–3).

Nevertheless, when both root canal therapy and retreatment fail or it is not feasible,

periapical surgery is often the only method of retaining teeth (4,5).

Periapical surgery enables complete debridement of the root canal and placement of a

root-end filling. This goal should be achieved by periapical resection, root-end cavity

preparation, and a bacteria-tight closure of the root canal system, preferably with a

biocompatible and bioactive retrograde filling (6,7).

In addition, the periapical pathological tissue should be completely debrided by

curettage to remove extraradicular infection, foreign body material, or cystic tissue (6).

Endodontic surgery has greatly benefited from continuing development and

introduction of new diagnostic tools, instruments and materials (6,8,9).

For many years, the state of the art was the traditional approach, performed by means

of root-end resection with a 45-degree bevel, retrograde preparation of the canal with

bur, and amalgam or intermediate restorative material (IRM) for root-end filling, with a

moderate success rate of approximately 60% (8,10,11).

The introduction of the dental operative microscope (DOM) in the early 1990 led to a

new phase in surgical endodontics (10). Besides magnification and illumination,

modern techniques incorporate also the use of ultrasonic tips, microsurgical

instruments and more biocompatible filling materials such as SuberEBA, and mineral

trioxide aggregate (MTA) (8–10). With regard to the outcome of apical surgery,

inconsistent success rates ranging from 44% to 90% were reported prior to the

introduction o microsurgical techniques (12). Nowadays, recent studies have shown

success rates that approached or exceeded 90% (13).

A root-end preparation should be parallel to the long axis of the root, 3mm deep, and

centered within the root, to offer adequate wall thickness and to retain a nontoxic

biocompatible filling material (14,15).

The advent of ultrasonic tips has enhanced this preparation, because of the availability

of tips with different shapes and angulations according to the root location (16,17). It

also brought numerous advantages (15) including smaller osteotomy, minimal or

inexistent bevel angles for root-end resection (18,19), thus reducing the number of

exposed dentinal tubules and consequently the possibility of apical leakage (16,20).

Moreover, they also enable the removal of isthmus tissue present between two canals

6

within the same root (20–22). With these tips, a better shaped root-end cavity, which is

more centrally placed and along the direction of the original root canal, smaller, cleaner

and more retentive, can be achieved (19,23).

The first root-end preparation using modified ultrasonic inserts after an apicoectomy is

attributed to Bertrand et al. (24). Since then, a large number of laboratory, but few

clinical studies have investigated different aspects including the crack formation

following root-end preparation (1).

Microcracks may increase the chance for apical leakage, and may jeopardize the

overall strength of the root end. Even though this has not been formally proven, their

occurrence constitutes a clinical concern (7,25,26). Apical resorption after healing may

eliminate the surface defects and contribute to the overall success of treatment. Also,

such defects can be removed by using finishing burs on the resected and retrofilled

root-end (20,27).

Root cracks after the use of ultrasound-activated tips have been detected using

different methods such as: visual magnification with or without the use of dyes

(1,28,29), histologic cuts (30), fluorescence confocal microscopy (30),

stereomicroscopy (7,22) and scanning electron microscopy (SEM) (16,17,25,31). They

are the consequence of several factors, such as the use of dehydrated extracted teeth,

absence of periodontal ligament, power settings of the ultrasound unit, and sputter-

coating of specimens for SEM examination (14,31–33).

Recently some attempts to improve the performance of ultrasonic instruments have

been made. The introduction of diamond-coated and zirconium-coated retrotips

represents an important issue in this field (31) as well as the new CVD® technology

(CVD-Vale, São José dos Campos, SP, Brazil): characterized by a thick layer of pure

diamond forming a single stone covers the entire surface of the tip (16,33). The aim of

this study is to evaluate the time requirements and features apical cavity preparation

performed with different ultrasonic tips from CVDentUS®: model TOF-2 and a prototype

tip.

7

MATERIALS AND METHODS

Specimen selection

Thirty-two freshly extracted single-rooted teeth were selected, with fully developed

apices. All teeth were immersed in 1% NaOCl solution for 15 minutes, immediately

after extraction. Afterwards, soft tissue and debris were removed from the surface of

the roots by hand scaling.

The integrity of the roots was determined by using a dental operating microscope -

DOM (Leica Microsystems© M300 DENT) at 16x magnification. Teeth were kept in

0,5% chloramine T during two weeks.

Specimen preparation

Teeth were decoronated using a high-speed diamond bur under continuous water

spray. The working length of the root canal was determined by observing the

emergence of a size 10 K-file at the foramen, measuring it and withdrawing 0,5mm.

Root canals were then cleaned and mechanically prepared up to F2 (ProTaper®

universal; Dentsply Maillefer, Baillaigues, Switzerland) by using a crown-down

technique. The canals were irrigated with 1mL of 1% NaOCl between each file, totaling

4mL. When the instrumentation was completed, the canals received a final flush with

2ml of 70% alcohol, and were dried with sterile absorbent paper points (Zipperer®

Absorbent Paper Points, Endo Easy Efficient®, Munich, Germany).

The root canal filling was performed with a single cone technique, using a calibrated

gutta-percha ProTaper® point F2 (ProTaper® universal; Dentsply Maillefer, Baillaigues,

Switzerland) and AH Plus® (Dentsply, DeTrey, Konstanz, Germany) as the sealer. The

gutta-percha cone was cut at the cement enamel junction (CAJ) with a warm

instrument and vertically warm condensed in the coronal portion with a Buchanan

System B Plugger (SybronEndo, California, USA).

Following obturation, each tooth was numbered and an X-ray image confirmed the

good quality of obturation. The coronal two thirds of the roots were mounted on high

viscosity silicone material - Coltène® Lab-Putty (Coltène/ Whaledent AG; Alstàtten,

Switzerland). During all subsequent procedures, teeth and respective silicone blocks

were stored in an incubator at 37oC and 98% humidity.

8

Apicoectomies

The section line was drawn at 3mm from the apex, and all the roots were resected at a

90o angle in respect to their longitudinal axis. Each tooth was sectioned using a H 23

LR® (Komet ,USA) carbide tungsten operative bur and then smoothed with a H 375 R®

(Komet, USA) carbide tungsten finishing bur

After apicoectomy, the teeth were checked to see the presence of any cracks and

fractures by one examiner under a DOM at 16x magnification. Photomicrographs were

made with a stereomicroscope (Nikon SMZ 1500) to the cutting plane of each root, first

without and then with methylene blue dye 1% (Canal blue - Dentsply, DeTrey,

Konstanz, Germany), applied directly to the surface during 5 minutes, and then rinsed

with abundant water during 1 minute, to simplify the visualization of cracks.

Preparation

The 32 teeth were randomly divided in two equal groups using stattrek.com (34),

according to the tips used to prepare the root-end cavity:

1: tip TOF-2 (CVDentus; Clorovale Diamantes Ind. E Com. Ltda Epp, São José

dos Campos, SP, Brazil);

2: tip prototype (CVDentus; Clorovale Diamantes Ind. E Com. Ltda Epp, São

José dos Campos, SP, Brazil);

Apical preparation was performed using the respective device, at the intensity

recommended by the fabricant (30% of power), under constant distilled water irrigation.

The specimens were kept in the putty silicone blocks and maintained wet throughout

the procedures. Each tip was used on a maximum of 8 roots.

Instrumentation was performed using intermittent and minimal pressure, with in-and-out

motion to start the preparation, then increasing the depth to 3mm from the resected

surface and finally moving it circumferentially to complete the entire preparation. This

was accomplished by a single experienced operator, under a DOM at 10x

magnification and it was considered finished when the operator determined the

preparation to be visibly free of debris. All preparations were class I (according to

Black’s classification). Time of preparation was measured using a stopwatch, counting

only the time of actual instrument contact with the root.

Photomicrographs were made to the preparation of each root first without and then with

methylene blue dye 1% (Canal blue - Dentsply, DeTrey, Konstanz, Germany), as

described previously.

9

Data analysis

The preoperative and the postoperative photomicrographs were coded and blinded,

and two examiners evaluated them.

The examiners assessed through the photomicrographs at 15x and 30x magnification:

The number, type and location (in relation to dentinal walls) of root surface

cracking;

The quality of root end cavity margins produced by ultrasonic retrotips;

And through direct stereomicroscope visualization at 40x magnification:

The presence of debris (superficial dentinal chips and/ or gutta-percha

remnants).

Microcracks were recorded by type, adapted from Rainwater et al. (29) and De Bruyne

et al. (19):

Incomplete cracks:

o Intracanal cracks - originating from the root canal and radiating into the

dentine;

o Extracanal cracks – originating from the root surface radiating to the

dentine;

o Intradentinal cracks – confined to the dentine.

Complete cracks: from the root canal to the root surface.

Also, it was checked if cracks were located either at the narrower or wider side of the

remaining dentine surface.

The quality of root end cavity margins (‘marginal integrity’) produced by ultrasonic

retrotip was assessed according to the following scores adapted from Taschieri et al.

(31):

0 – The ideal preparation (0 defects);

1 – A single visible defect produced by the contact between the angle of the tip

and the cavity margin;

2 – Chipped, ragged cavity margin;

3 – Chipped, ragged cavity margin plus some defects due to the tips bouncing

off the root face during root end preparation.

The presence or absence of debris (superficial dentinal chips and/ or gutta-percha

remnants) in the cavity (‘quality walls’) was classified according to the following scores

adapted from Khabbaz et al. (1):

0 – Clean walls

1 – Debris on 1 wall

10

2 – Debris on 2 walls

3 – Debris on 3 walls

4 – Debris on 4 walls.

The scores and number of cracks in each root were assessed independently by two

investigators. If the scores did not agree, they assessed again the images until a

consensus was reached.

Statistical analysis was carried out to evaluate the difference between groups using a

software package (SPSS).

In order to evaluate the incidence of microcracks before and after retropreparation,

results obtained for each group were analyzed by Wilcoxon test.

Mann-Whitney test was carried out to verify the difference in microcracks, marginal

integrity and quality walls between groups.

In order to determine the statistically significant differences after the intervention,

relative to the number of microcracks at the widest and narrowest part of the root-end,

a binomial test was carried out with a cutoff point of 50%.

To evaluate if the difference in time preparation between groups was statistically

significant, a Mann-Whitney test was used. The possible association between the

number of microcracks and time was evaluated by means of Spearman's rank

correlation coefficient.

Ultrasonic tips analysis

One sample of each ultrasonic tips tested (before and after use) was analyzed under

scanning electron microscopy (SEM).

11

RESULTS

Table I shows the results of statistical analysis calculated in the two groups regarding

the number, type and location of cracks, and some representative images are in annex

(figures 1 and 2). The majority of the roots had no visible cracks after root resection,

although microcracks were observed in three roots, belonging to group 2 - one root

with two intracanal cracks and the other two roots with one intradentine crack each

one. After root-end preparation, the roots that exhibited intradentine cracks developed

extension of these cracks (one root developed an intracanal crack and the other root

an extracanal crack). Of the 29 roots that did not have cracks after root-end resection,

2 roots for the group 1 and 6 roots for the group 2 showed the formation of new cracks

after the root-end preparation procedure. Of the 8 roots that developed new cracks,

only one root had an intradentine crack, while the other 7 roots had intracanal cracks

(in a total of 10). No complete cracks were found.

Table I – Statistical analysis calculated in the two groups regarding the number, type and

location of cracks.

Group 1 (TOF-2) Group 2 (Prototype)

Before

Number of cracks

x /dp/max/min

0/0/0/0 0.25/0.58/2/0

Type of cracks

intracanal/extracanal/intradentine/complete 0/0/0/0 2/0/2/0

Location of cracks

narrower/wider 0/0 1/3

After

Number of cracks

x /dp/max/min 0.13/0.34/1/0 0.81/0.83/2/0

Type of cracks

intracanal/extracanal/intradentine/complete 1/0/1/0 12/1/0/0

Location of cracks

narrower/wider 0/2 2/11

In group 1, no statistical significant differences were found (Z = -1414, p = 0.157) in the

number of cracks before and after preparation, whereas in group 2, there are

statistically significant differences (Z = -2251; p = 0.024) before and after. Graph 1

shows the variation of the estimated marginal mean for the two groups.

12

Graph 1 – Variation of the estimated marginal mean for the two groups.

At the moment ‘before' there are no statistically significant differences (U = 104.00, Z =

-1789, p = 0.074) in the number of microcracks in the two groups. However, at the time

'after', there are statistically significant differences (U = 68.00, Z = -2692, p = 0.007) in

the number of microcracks comparing the two groups.

Regarding the ‘marginal integrity’ (table II), most teeth were scored as ‘0’, and the

maximum value was ‘2’ (one root in group 1 and two roots in group 2). Moreover, we

cannot observe statistically significant differences (U = 110.00, Z = -0.767, p = 0.443)

between both groups.

Table II – Frequency and percentage calculated in group 1 (TOF-2) and group 2 (prototype)

regarding the ‘marginal integrity’.

Frequency %

Group 1 Group 2 Group 1 Group 2

0 10 8 62,5 50,0

1 5 6 31,3 37,5

2 1 2 6,3 12,5

Total 16 16 100,0 100,0

13

In our evaluation of the ‘quality walls’ (table III), most teeth were also scored as ‘0’, and

the maximum value was ‘1’ (three roots in group 1 and four roots in group 2). There

aren’t also statistically significant differences (U = 120.00, Z = -0421, p = 0.674)

comparing the two groups.

Table III – Frequency and percentage calculated in group 1 (TOF-2) and group 2 (prototype)

regarding the ‘quality walls’.

Frequency %

Group 1 Group 2 Group 1 Group 2

0 13 12 81,3 75,0

1 3 4 18,8 25,5

Total 16 16 100,0 100,0

The frequency of microcracks observed in the widest part of the root was 87% which

was significantly different from the frequency of microcracks observed at the narrowest

part (p = 0.007).

Table IV presents some statistical values regarding the instrumentation time. No

statistically significant differences (U = 98.00, Z = -1133, p = 0.257) of the time

between the groups tested were found, and there is no correlation (CC = 0.184, p =

0.314) between time of preparation and number of microcracks.

Table IV - Minimum, maximum, mean and standard deviation (SD) calculated in the two groups

regarding the intrumentation time.

Minimum Maximum Mean SD

Group 1 11,0 60,3 38,644 15,1320

Group 2 29,0 82,8 48,513 17,7394

One of the prototype tips (group 2) fractured at the second use, being substituted with

a new one, which was used in seven roots.

Figure 1 and 2 depicts the images of the ultrasonic tips obtained by SEM examination,

before and after 8 retropreparations, respectively.

14

a)

b)

Figure 1: a) – TOF-2 tip before use (40x magnification); b) - Prototype tip before use

(40xmagnification).

a1)

b1)

a2)

b2)

Figure 2: a1) / a2) – TOF-2 tip after use (40x and 100x magnification); b1) / b2) - Prototype tip

after use (40x and 100x magnification).

15

DISCUSSION

Since the introduction of ultrasonic tips for root-end cavity preparation during

endodontic surgery in the 1990’s, several studies have compared this strategy with

conventional root-end cavity preparation using rotary burs in a microhandpiece.

Many authors (1,2,15,35–38) have confirmed the technical improvement afforded by

ultrasound – the specific advantages being: (a) beveling: unnecessary reduction of the

corono-root proportion is avoided, and the risk of periodonto-endodontic

communication is minimized, with preservation of the dental and bone structure,

securing an improved environment for healing; (b) cavity preparation: a smaller bony

access is required, with easier buccolingual extension, parallel to the long axis of the

root.

A great concern to the clinician is the formation of cracks or microfractures following

root-end resection or root-end preparation. The significance of root-end cracking would

seem to be increased susceptibility to root fracture, the inability to seal the root-end

preparation properly, and the possibility of additional site of bacterial contamination

(26). The frequency of root-end cracking during apical preparation has been

investigated extensively, and is the object of our study.

Some studies results indicate that ultrasonic devices are responsible for generating

cracks at the root-end surface (14,26,36,39) but other results indicate the opposite

(21,38,40,41).

Wuchenich et al. (37) compared ultrasonic and bur root-end cavity preparations with

regard to cleanliness and root canal parallelism, and found that cavities prepared with

ultrasonic tips were cleaner, deeper, and had more parallel walls than those prepared

by burs. However, these authors did not refer to microfractures.

Almost all later studies have demonstrated microfractures in the roots of extracted

teeth in which root-end cavities were prepared with ultrasonic tips

(1,17,19,23,25,29,31,42). It is possible that the propagation of the observed

microfractures was enabled by the in vitro conditions in which these studies were

performed: dehydration, lack of periodontal support, stresses exerted during extraction,

inappropriate storing, and careless handling of the extracted teeth (4,7,21,39).

Therefore, in the present study we could have obtained an overestimation of cracks,

despite all the efforts that have been made to prevent this - only freshly extracted teeth

were used and attention was paid to keep the samples moist during the root-end

preparations, as suggested by other authors (31).

16

Abedi et al. (14) compared root-end cavities prepared with bur and with ultrasonic tips

attached to two different ultrasonic units. Their findings showed a significantly higher

incidence of crack formation in the walls of root-end cavities prepared by ultrasonic

tips, and the average time for preparation was also greater (2 minutes against 10 to 15

seconds in the bur group). They concluded that the formation of cracks is a function of

the power of the unit, time of application, presence or absence of preoperative

microcracks, and the thickness of surrounding dentin, indicating that ultrasonic tips

shouldn’t be applied to thin walls (<1mm).

Other in vitro study (22) compared the quality of root-end preparations between

ultrasonic retrotip and conventional microhandpiece bur. They analyzed the shape and

size of preparation, as well as the loss of tooth structure after root-end preparation,

under a stereomicroscope in association with an image processing system. The results

were significantly better for the ultrasonic group, which produced more conservative

and less perforated cavities.

Lloyd et al. (41) reported poorer results with ultrasound versus micro-handpieces and

burs, due to the appearance of marginal cracks.

In a clinical study (3), the overall success rate in the ultrasound group was 80,5% and

in the group treated with a bur was 70,9%. In molars, the difference in success rate

was significant. They concluded that the use of an ultrasonic device in apical surgery

improved the outcome of treatment, but the main disadvantage is microfractures and

chipping.

In other retrospective evaluation (43), there was also a great difference in outcome of

treatment in favor of the ultrasonic technique (85% versus 68%).

On a clinical and radiological study (44) the results were obtained with different

periapical surgical techniques, and the better clinical and radiological success rate after

one year was achieved when ultrasound was used for root-end preparation, comparing

with rotary instruments (conventional technique).

To avoid artifacts and to obtain results clinically more relevant, some authors argue

that investigations should preferably be performed in situ (2,7,19,26,30).

Min et al. (30) suggested that the use of cadavers might be more clinically relevant.

They concluded, by histologic examination, that root-ends prepared with ultrasonic

devices had a statistically greater number of fractures than both the control and

conventional (microhead handpiece) groups. On the other hand, confocal microscopic

evaluation did not show significant differences, and the argument was that the

17

magnification used (40x) did not permit the differentiation of preexisting fractures: all

fractures were included in the statistical analysis, while in the histologic study, fractures

considered as preexisting due to the presence of sealer particles in the cracks were

excluded.

Other study that used human teeth in cadavers (2) compared ultrasonic and high-

speed bur root-end preparations in relation to the size of bony crypt, the minimum

depth of root-end filling, the length of the root-end filling along the resected root

surface, and the root-end resection bevel angle, concluding that ultrasonic root-end

preparations are significantly better considering these aspects (deeper root-end

preparation, less bevel, maintain the direction of the canal space and less bony crypt

size).

Regarding the presence of microfractures, Calzonetti et al. (7) suggested that in situ,

roots may absorb some of the ultrasonic impact and prevent the propagation of

microfractures, circumventing the tooth desiccation and brittleness associated with

work in vitro and thus reduce the chance of artifacts. In fact, they did not find any

microfractures after ultrasonic root-preparation. This agrees with the results obtained

by De Bruyne and De Moor (19), which found the amount of cracking to be statistically

different between extracted and cadaver teeth (fewer cracks).

Gray et al. (26) compared the frequency of cracking and chipping in cadaver and

extracted teeth under scanning electron microscopy with indirect resin replicas using a

high-speed bur or an ultrasonic tip at either high or low intensity. The results did not

show significant difference between any groups in terms of cracking of root-ends. The

only significant difference was seen in extracted teeth where ultrasonic preparation

caused more chipping than rotary preparation. Varying the intensity was not significant.

This was also supported by other studies: manipulation at high power also did not

produced a large number of microcracks (23,40). On the contrary, these results do not

agree with several studies - significantly more canal cracks per root occurred when the

ultrasonic tip was used on the high-frequency setting for root-end preparation than

when the ultrasonic tip was used on the low power setting (31,39,40).

In the present study we did not vary the intensity of the power setting, as we always

used the value recommended by the manufacturer (30% of the maximum power).

Further research is required to determine the optimum power for root-end preparation

with the tips tested on this study and with in situ conditions.

Layton et al. (39) observed fractures after high-speed cavity preparation, a

phenomenon not observed at low speeds (100 to 200mHz less than the high-speed).

18

They observed three types of cracks on the resected root-ends: canal cracks,

intradentin cracks and cemental cracks. In contrast, Chou et al. (38) reported fewer

fissured teeth with ultrasound than with micro-handpiece.

Rainwater et al. (29), besides intracanal and extracanal cracks, also found

communicating cracks, without significant differences between the three groups:

conventional ultrasonic (CUS) tips, diamond-coated ultrasonic (DUS) tips, and high-

speed stainless-steel burs (HSB). They argued that even though the majority of the

cracks were not observed after root resection, disruptions could have been made

during this process that became apparent during the root-end preparation. They also

studied the dye penetration and found no difference between DUS and CUS.

Waplington et al. (40) noted chipping on all the ultrasonically prepared root-end

cavosurface margins. On the contrary, the bur prepared group did not show cracks or

chipping. Engel et al. (21) reported more centered and smaller preparations on the

canals and isthmus, with the ultrasonic device comparing to the burs. On the other

hand, traditional and combined techniques resulted in greater debridement. They claim

that ultrasound might be a useful adjunct to surgical endodontics, particularly in cases

where a high risk of perforation exists or when limited access to the root apex is a

considerable constrain. Moreover, ultrasound preparations are more conservative and

deeper (22). The increased cavity depth that can be achieved with ultrasonic tips might

be a significant factor for controlling apical leakage (1).

Therefore, the only apparent inconvenience is the presence of microfractures. Cracking

and chipping may lead to long-term failure of the surgical procedures because of

increasing risks for apical leakage (1,31). This issue needs to be evaluated in further

leakage studies to clarify the relation of chipping to long-term sealing at the apex. In

fact, the influence of root-end microfractures on the periradicular healing process and

apical leakage should be clarified (25).

Diamond-coated tips have been introduced in the hope of minimizing dentinal fractures

through their ability to abrade dentine more quickly, reducing the time that the

instrument spends in contact with the root-end (45,46). Although, no significant

differences concerning microfractures or marginal chipping among stainless steel,

diamond coated and zirconium coated tips have been observed (23,29,45,47). New

ultrasonic tips for apical preparation continue to be studied, developed and introduced

on the market, such as Jetip, which is made completely of stainless steel (17), and

CVD (16,48), which was the subject of research in the present study.

19

The direct CVD diamond deposition on molybdenum tips allows a fabrication process

that exhibits high adhesion characteristics of the diamond coating (49). This new

technology deposits a thick layer of pure diamond, forming a single stone that covers

the entire surface of the tip, (16).

In a study by Bernardes et al. (16), they compared three different ultrasonic diamond

tips. They verified that Satelec and Trinity tips, which have small-sized diamond

crystals embedded in a joining material, have losses in the amount of diamond after

utilization, something which was not verified with CVD tips. These tips have been

shown to have a greater cutting efficiency than conventional ultrasonic diamond tips

and presented the shortest root-end cavity preparation time compared with other

brands of ultrasound-activated diamond tip (16,48). These results were corroborated by

other study that used CVD tips in apical preparation without any injury to the root-end

surface (33).

This in vitro study investigated the effect of two different ultrasonic retrotip surfaces

related to the number, type and location of cracks, the quality of root end cavity

margins, the presence or absence of debris, and the time of preparation.

Despite the study of Beling et al. (50), where no significant difference with regard to the

number or type of cracks after root-end resection or root-end preparation was found

between gutta-percha filled and uninstrumented roots, it was considered better to root

fill the teeth first, because it reproduces the clinical situation, and because we wanted

to evaluate the presence of gutta-percha remnants in the cavity walls.

It was observed that after the extraction procedure of the cadaver roots, a number of

extra cracks arose, indicating that the extraction procedure damaged the roots before

root-end resection and preparation (19). As such, the use of a fixing apparatus to

minimize the absence of periodontal ligament, as suggested in the study by Gondim et

al. (25) to reduce the chances for artifacts would not suffice.

Despite this fact, an effort was done in our research to simulate the periodontal

ligament support of the root to be prepared by using putty silicone blocks. Other study

used resin blocks (1). As mentioned before, the effect of these mechanisms in the

prevention of microfractures has not been proven.

Methylene blue dye was used in this study, as it has been shown by Cambruzzi et al.

(51) to be an aid in the detection of fractures. Methylene blue was used to decrease the

20

optical activity of dentin and to stain cracks for easier microscopic identification,

although this was not verified.

1. Number, type and location of cracks

The incidence of microcracks in this study was 12,5% for group 1 and 56,25% for

group 2. These results do not correspond with the study of Bernardes et al. (16), who

reported no incidence of cracks or fractures in any specimen (they used three different

diamond tips, including CVD).

An incidence of 2,1% was found in the study of Peters et al. (42), who used ultrasonic

diamond-coated or stainless steel smooth retrotips to prepare 48 root-end cavities in

molar teeth mimicking clinical conditions. Teeth were examined under SEM and craze

lines, visible at 300x magnification or higher, were not considered microcracks.

Microcrack incidence of 16,95%, 28,85% and 41,6%, respectively, was found at

magnifications of 25x, 50x and 30x when root-ends were prepared ultrasonically

(7,14,36)

Although it has been reported that the number of microcracks on the resected surfaces

increased after preparation with ultrasonic retrotips, Ishikawa et al. (23) only found four

microcracks (not defining the type) in eighty-five teeth, that were evaluated by SEM.

Their possible explanation for such low rate of cracks is the use of a saline bath during

preparation.

Khabbaz et al. (1) did not found any cracks at close inspection immediately after cutting

the root apex, and after the root-end cavity preparation all cavities were photographed.

No complete cracks were found. Small intradentinal cracks were detected in 7% of the

small roots of group A (micromotor), 20% of the large and 21% of the small roots in

group C (ultrasonic smooth). Groups B (ultrasonic diamond) and D (sonic diamond) did

not showed any cracks.

Taschieri et al. (31) found 20 out of 45 teeth with cracks under evaluation with SEM

photographs at magnification of 48x and up to 1550x if the two blind examiners did not

agree. Only the specimens treated with a stainless steel retrotip at half power did not

show complete or incomplete dentinal fractures. Conversely, three complete canal

fractures were found when using diamond tips at the full power setting. However, no

significant differences were found between diamond tips and stainless steel at both

power settings tested.

Rainwater et al. (29), using a stainless steel and a diamond retrotip and setting the

ultrasonic device at low power, found no significant difference between the two kinds of

21

tips for both the number and the type of cracks. Most cracks consisted of intracanal or

extracanal types, and a lower number were of communicating type.

In the present study, most microcracks consisted of intracanal type, and no complete

(communicating) cracks were found.

It is difficult to compare the results of studies with dissimilar experimental design. In

fact, the use of different types of retrotip design, materials and evaluation methods,

represents an important source of variability. Different apical diameter of the specimens

used in the various studies could also lead to increased variability in outcomes. Until

standardization in experimental study design is achieved, the comparison between

different reports may lead to biased conclusions.

In our study, we found microcracks before ultrasonic preparation, which was also found

in previous studies (39,50). In contrast, the preoperative analysis in other studies refer

no cracks or marginal chipping during resection alone (1,25).

In the present study, we found more cracks in the wider dentine walls -13- than in the

narrower walls -2-, which is statistically significant and is in agreement with the results

obtained by De Bruyne et al. (19), where only few cracks were situated at the narrower

side of the remaining dentine. This was in contrast to results of former studies, where

most cracks developed in the thinnest walls surrounding the root-end cavity

preparations (14) or small diameter roots developed more cracks (52). As no limitation

time was set, it could be that the time of preparation may have contributed to the

number of cracks.

During evaluation of the images it was observed that existing cracks sometimes did

enlarge after apical preparation. This fact was also documented in other studies

(19,29).

Magnification

Magnification is a factor to be considered in the detection of microfractures. Some

studies use low magnifications (x16-50), which might prevent the detection of existing

microfractures (4,40). In the present study, we used low magnification (10x) during the

apical preparation, because in clinical practice it is very difficult to attain a good field of

view with magnification. We used magnifications (15x, 30x and 40x) which proved to be

enough for the details we wanted to evaluate. Although, according to Gondim et al.

(25), the use of higher magnification (x150) caused a significant increase (more than

double) in the number of microfractures detected.

Studies that compare the impact of magnification in different evaluation methods are

needed.

22

2. Quality of root end cavity margins (marginal integrity) and presence or

absence of debris (quality walls)

Apart from cracks, chipping was also referred as a consequence of ultrasonic or sonic

root-end preparation (1,19,25,26,40,41). The importance of chipped margins is unclear

but it may affect the marginal seal produced when a root-end filling is placed.

Few teeth showed chips between the angle of the tip and the cavity margin or ragged

margins, as well as debris in the cavity walls. This is in contrast with the results

obtained by Khabbaz et al. (1), where all methods produced dentine chips in the walls

of cavities. However, the amount of produced debris was significantly different, with

values ranging from 0 to 90%, with the highest frequency on the cavity walls prepared

with the bur on the micro contra angle slow-speed handpiece, which may be attributed

to the fact that preparations were made under no water spray, whereas the sonic and

ultrasonic tips were supported by irrigation.

The effects of residual gutta-percha remnants on treatment outcome are unknown and

require further clinical studies. Bernardes et al. (16) found fewer regular preparations

with CVD tips, comparing with Satelec and Trinity tips. This is in accordance with the

present study, where cavity walls were clean and free of debris in most cases.

In the present study, very few chipped margins were found. Taking this fact into

consideration, no correlation may be attempted with preparation time. This result is in

accordance with the findings of Taschieri et al. (31). It is possible that the longer the

preparation time the higher the chance of producing chipped margins, but this issue

needs further investigation.

3. The instrumentation time

Time of preparation in the clinical practice is something to take into high consideration

(1,21,23,36,40,42).

A longer instrumentation time was necessary for group 1, possibly because the cutting

efficiency of these tips is lower than the prototype tip due to a smaller diameter.

The mean time was higher when compared with the study of Bernardes et al. (16), who

found the following mean times for apical cavity preparation: 45,57s (Satelec), 44,83s

(Trinity), 17,94s (CVD). Nevertheless, these values are very low comparing with other

studies.

Ishikawa et al. (23) reported 181,80s (KiS), 204,60s (CT-5), 69,10s (diamond-coated).

Engel and Steiman (21) found that preparation time with bur was similar to that of

smooth ultrasonic tips.

23

Peters et al. (42) reported that, using diamond-coated and smooth ultrasonic tips, the

preparation times ranged from 25 to 361 seconds and were significantly lower for the

diamond-coated that the stainless steel smooth ultrasonic tips. They also found a

correlation between the incidence of cracks and the time needed to accomplish root-

end preparation. In the present study no correlation was observed between preparation

times and the incidence of cracks using the given power setting.

Khabbaz et al. (1) found that the time needed to prepare a root-end cavity with rotary

instrumentation was very short compared to the sonic and ultrasonic tips, which agree

with Waplington et al. (40), who found that the rotary preparation is more rapid than the

ultrasonic one. However, in clinical practice, sonic or ultrasonic instruments may be

faster because they have better accessibility to the root-end and require less bone

removal.

Taschieri et al. (31) observed that cavity preparation with diamond-coated retrotips is

faster that stainless steel ones.

4. Tips evaluation

The robustness to use of CVD tips presented by the only study that compare these

new tips in retropreparation (16) was not verified. In fact, by SEM analysis it is possible

to verify the surface alteration of the tips, with loss of particles (smoothness of the

surfaces) particularly in the active point. Besides that, during the active cutting process,

one prototype tip (group 2) fractured. The same happened in other studies. Paz et al.

fractured two ET-20D tips and attributed this to the thinner makeup of the ET-20D tip in

comparison with the CPR-2D. This was also in agreement with Walmsley et al. (53)

who found in their study that thinner tips were more prone to fracture during cutting.

24

CONCLUSIONS

Based on the conditions of this study, the following conclusions can be drawn.

1. Cracks were produced at the root-end face, mainly when the prototype

ultrasonic retrotip was used, with statistically significant differences. Due to the

high amount of cracks produced with the prototype tip, its use in apical

preparation is questionable, although more studies are needed, particularly with

in situ conditions.

2. No significant differences were found regarding the location and type of cracks.

3. The marginal quality, as also as the quality of the cavity walls was very good for

both tips tested. No significant differences were found comparing the results of

the prototype and TOF-2 tips regarding these parameters.

4. Prototype ultrasonic tip was faster than TOF-2 tip for the given power setting

(recommended by the fabricant), but the difference is not statistically significant.

25

AKNOWLEDGMENTS

I want to thank all my teachers, who guided me trough this wonderful world of dentistry,

and made me love this art.

Particularly, I would like to express my deep gratitude to my advisors, Master Paulo

Palma and Doctor João Miguel Santos, for all the help, advice, collaboration and

promptitude during the elaboration of my thesis. They have triggered my great interest

in Endodontics, and I have learned a lot from them.

I also want to express my gratitude to Master Rui Isidro Falacho for his support, and to

Master Francisco Caramelo, who gave me an essential aid regarding the statistical

analysis.

I am also greatful to CVDentus®, who provided the necessary material for this study.

Finally I want to thank my parents, who gave me dreams and to my brother, who

showed me that is possible to reach them.

26

ANNEXES

a)

b)

c)

d)

Figure 1: Photomicrographs of one tooth belonging to group 2, before (a, c) and after (b, d)

root-end cavity preparation. Two intracanal cracks are visible before (arrows in c), and they

become evident after root-end cavity preparation (arrows in b and d).

27

a)

b)

c)

d)

Figure 2: Photomicrographs of one tooth belonging to group 1, before (a, c) and after (b, d)

root-end cavity preparation. No cracks are visible before, and one intradentine crack becomes

evident after root-end cavity preparation (arrow in b and d).

28

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